The present invention relates generally to regulating apoptosis, and more particularly to the novel aspartate-specific cysteine proteases known as caspases, their coding regions, mutant forms thereof, and their use in screening assays and as pharmaceutical compositions for the controlled death of targeted cells to treat human disease.
Tissue homeostasis is maintained by the process of apoptosisxe2x80x94that is, the normal physiological process of programmed cell death. Changes to the apoptotic pathway that prevent or delay normal cell turnover can be just as important in the pathogenesis of diseases as are abnormalities in the regulation of the cell cycle. Like cell division, which is controlled through complex interactions between cell cycle regulatory proteins, apoptosis is similarly regulated under normal circumstances by the interaction of gene products that either prevent or induce cell death.
Since apoptosis functions in maintaining tissue homeostasis in a range of physiological processes such as embryonic development, immune cell regulation and normal cellular turnover, the dysfunction or loss of regulated apoptosis can lead to a variety of pathological disease states. For example, the loss of apoptosis can lead to the pathological accumulation of self-reactive lymphocytes that occurs with many autoimmune diseases. Inappropriate loss or inhibition of apoptosis can also lead to the accumulation of virally infected cells and of hyperproliferative cells such as neoplastic or tumor cells. Similarly, the inappropriate activation of apoptosis can also contribute to a variety of pathological disease states including, for example, acquired immunodeficiency syndrome (AIDS), neurodegenerative diseases and ischemic injury. Treatments which are specifically designed to modulate the apoptotic pathways in these and other pathological conditions can alter the natural progression of many of these diseases.
Although apoptosis is mediated by diverse signals and complex interactions of cellular gene products, the results of these interactions ultimately feed into a cell death pathway that is evolutionarily conserved between humans and invertebrates. The pathway, itself, is a cascade of proteolytic events analogous to that of the blood coagulation cascade.
Several gene families and products that modulate the apoptotic process have now been identified. One family is the aspartate-specific cysteine proteases (xe2x80x9ccaspasesxe2x80x9d). The caspase Ced-3, identified in C. elegans, is required for programmed cell death during development of the roundworm C. elegans. Ced-3 homologues as well as other caspases have been characterized. The human caspase family includes, for example, human ICE (interleukin-1-xcex2 converting enzyme) (caspase-1), ICErelII (caspase-4), ICErelIII (caspase-5), Mch5 (caspase-8), Mch4 (caspase-10), ICE-LAP6 (caspase-9), Mch2 (caspase-6), CPP32 (caspase-3), ICE-LAP3 (casepase-7), ICH-1 (caspase-2), Caspase 11-14, and others.
The caspases share many features. In this regard, caspases are cysteine proteases (named for a cysteine residue in the active site) that cleave substrates at Asp-X bonds. Furthermore, the primary caspase product is a zymogen that requires proteolytic cleavage at specific internal aspartate residues for activation. The primary gene product is arranged such that the N-terminal peptide (prodomain) precedes a large subunit domain, which precedes a small subunit domain. Cleavage of a caspase yields two subunits, a large (generally approximately 20 kD) and a small (generally approximately 10 kD) subunit that associate non-covalently: to form a heterodimer, and, in some caspases, an N-terminal peptide of varying length (see FIG. 1). The heterodimer may combine non-covalently to form a tetramer.
Caspase zymogens are themselves substrates for caspases. Inspection of the interdomain linkages in each zymogen reveals target sites (i.e. protease sites) that indicate a hierarchical relationship of caspase activation. By analyzing such pathways, it has been demonstrated that caspases are required for apoptosis to occur. Moreover, caspases appear to be necessary for the accurate and limited proteolytic events which are the hallmark of classic apoptosis (see Salvesen and Dixit, Cell, 91:443-446, 1997). However, when overexpressed in mammalian cells, the short prodomain caspases-3 and -6 cells are unable to undergo autocatalytic processing/activation and do not induce apoptosis. Thus, no cellular model system has been developed in which to test inhibitors of these caspases nor is gene delivery of a caspase commonplace.
Therefore, there exists a need in the art for methods of assaying compounds for their ability to affect caspase activity as well as for methods of regulating caspases in order to treat diseases and syndromes. The present invention provides recombinant caspase constructs that are active in cells, allowing the regulation of apoptosis for the treatment of pathology as well as providing methods and compositions for assaying compounds for caspase inhibitory and, thus, anti-apoptotic effects, while further providing other related advantages.
The present invention generally provides rev-caspases. In one aspect, the invention provides an isolated nucleic acid molecule encoding a rev-caspase. In certain embodiments, the rev-caspase is selected from the group consisting of rev-caspase-1, rev-caspase-2, rev-caspase-3, rev-caspase-4, rev-caspase-5, rev-caspase-6, rev-caspase-7, rev-caspase-8, rev-caspase-9, rev-caspase-10, rev-caspase-11, rev-caspase-12, rev-caspase-13, and rev-caspase-14. In other preferred embodiments, the rev-caspase is a human rev-caspase. Nucleic acid and amino acid sequences of rev-caspases are provided. The invention also provides rev-caspase proteins.
In another aspect, an expression vector comprising the nucleic acid molecule encoding rev-caspase is provided, wherein the sequence encoding rev-caspase is operatively linked to a promoter. In certain embodiments, the promoter is inducible, such as HIV LTR. Host cells transfected with the expression vectors are also provided.
In the present invention, methods of identifying an inhibitor or enhancer of caspase processing activity are provided, comprising: (a) contacting a sample containing an in vitro translated rev-caspase with a candidate inhibitor or candidate enhancer; and (b) detecting the presence of large and small subunits of rev-caspase, and therefrom determining the level of caspase processing activity, wherein a decrease in processing indicates the presence of a caspase inhibitor, and wherein an increase in processing indicates the presence of a caspase enhancer, wherein processed rev-caspase yields large and small subunits.
In other aspects, methods are provided for identifying an inhibitor or enhancer of caspase processing activity, comprising: (a) contacting a cell transfected with the vector expressing rev-caspase with a candidate inhibitor or candidate enhancer; and (b) detecting the presence of large and small subunits of rev-caspase, and therefrom determining the level of caspase processing activity, wherein a decrease in processing indicates the presence of a caspase inhibitor, and wherein an increase in processing indicates the presence of a caspase enhancer, wherein processed rev-caspase yields large and small subunits.
Methods are also provided for identifying an inhibitor or enhancer of caspase-mediated apoptosis, comprising: (a) contacting a cell transfected with the vector expressing rev-caspase with a candidate inhibitor or candidate enhancer or with a reference compound; and (b) detecting cell viability, wherein viability of cells contacted with a candidate is increased in the presence of an inhibitor and is decreased in the presence of an enhancer compared to cells contacted with a reference compound.
In other aspects, gene delivery vehicles, comprising the nucleic acid molecule encoding a rev-caspase are provided, wherein the rev-caspase sequence is operatively linked to a promoter. In preferred embodiments, the gene delivery vehicle is a retrovirus or adenovirus or the nucleic acid molecule is associated with a polycation. The gene delivery vehicle may further comprise a ligand that binds a cell surface receptor.
The invention also provides methods of treating cancer or autoimmune diseases, comprising administering to a patient the gene delivery vehicles disclosed herein.
These and other aspects of the present invention will become evident upon reference to the following detailed description and attached drawings. In addition, the various references set forth below that describe in more detail certain procedures or compositions (e.g., plasmids, etc.), and are therefore incorporated by reference in their entirety.